1. Field of the Invention
The present invention generally relates to a composition for treating hearing loss. More specifically, the composition includes components that provide an additive effect that is equal to or greater than the sum of the effects of the individual components.
2. Description of the Related Art
Extensive studies have been performed on compositions for treating side effects to antibiotic treatment, along with methods of treating the side effects using various compositions. Particularly problematic side effects from antibiotic treatment include kidney damage, loss of balance, and hearing loss attributable to antibiotic treatment such as aminoglycoside or glycopeptide antibiotic treatments. The damaging side effects of many aminoglycoside antibiotics were first reported in the 1940s, and the damaging side effects have long been an impediment to use of aminoglycoside antibiotics. Aminoglycoside antibiotics cause permanent deficits in the vestibular system (balance) and irreversible cell death in the cochlea, resulting in hearing impairment.
While the damaging side effects of aminoglycoside antibiotics, in particular, have impeded their use, it has not eliminated their use. Aminoglycoside antibiotics are the only “standard of treatment” in certain severe gram-negative bacterial infections, and the only inexpensive antibiotics that are available in developing countries. In the USA and European countries where the side effects are well recognized, and where 2nd and 3rd generation antibiotics are substituted wherever possible, side effects such as inner ear damage and hearing loss in patients can be minimized through careful monitoring of aminoglycoside antibiotic treatment. However, in countries in which there are fewer alternative drugs and monitoring is less rigorous or non-existent, side effects associated with aminoglycoside antibiotic treatment is more prevalent.
Notably, HIV death is often driven by tuberculosis as a secondary infection to HIV. In developing countries, aminoglycoside antibiotic treatment is widely used against tuberculosis. Given the generally lax monitoring and the high incidence of side effects associated with aminoglycoside antibiotic treatment in developing countries, poor patient compliance in completing proscribed aminoglycoside antibiotic treatment is common, contributing to the development of drug-resistant strains of tuberculosis.
Historically, from the first identification of side effects such as hearing loss attributable to aminoglycoside antibiotic treatment in the 1940s, research focused on identification of the aminoglycoside-induced pathophysiology and otohistopathology, the pharmacokinetics of the aminoglycoside antibiotics, and methods of monitoring early damage and thereby avoiding serious side effects attributable to aminoglycoside antibiotic treatment in humans. Mechanistic studies of aminoglycoside ototoxicity began in the 1980s. Findings that free-radical formation played a role in aminoglycoside ototoxicity were first indicated by reports of efficacy of some free radical scavengers in reducing ototoxicity. More direct evidence was uncovered in the mid to late 1990s of free radical formation by gentamicin (which is one type of aminoglycoside antibiotic), while ototoxicity attributable to aminoglycoside treatment was found to be inversely related to glutathione levels (endogenous antioxidant) in inner ear tissues. It has since been shown that ototoxicity of aminoglycoside antibiotics could be reduced by treatment with some radical scavengers.
Free radical formation has been shown to play a role in many instances of stress-induced cell pathology. High intensity noise has been shown to induce free radical formation. For the inner ear, the mechanism by which high intensity noise induces cell death in the cochlea and hearing impairment has been shown to be dependent on free radical formation. Noise-induced trauma to the inner ear has been shown to be inversely related to endogenous levels of glutathione in cochlear tissues.
The parallels between the mechanisms of noise- and antibiotic-induced cell death in the inner ear suggest that they share a common cell death pathway such that it is natural to speculate that agents found effective to attenuate noise-induced hearing loss may be effective to attenuate antibiotic-induced hearing loss. However, it is clear from the literature that great variability is found in the efficacy of some of the agents to reduce the damaging side effects of aminoglycoside antibiotics. To some extent, the variable efficacy may reflect differential mechanisms of action of the scavengers or unique molecular structures of the free radicals formed. Some agents have been tested for efficacy against noise-induced hearing loss (NIHL) and their relative efficacy has been found to differ from their relative efficacy for drug-induced hearing loss. For example, allopurinol is ineffective in reducing gentamicin-induced ototoxicity, but is effective in reducing noise-induced hearing loss. Given such observations (and other similar ones in literature), there is no substantial basis for believing that a formulation for treating noise-induced hearing loss will be effective to treat antibiotic-induced hearing loss and other side effects of antibiotic treatment.
In view of the foregoing, there remains further opportunities to develop effective methods of treating side effects of antibiotic treatment, including antibiotic-induced hearing loss, kidney damage, and loss of balance, the methods including the step of administering a composition that includes a specific combination of components, in biologically effective amounts, in conjunction with administration of antibiotics that are capable of causing side effects such as hearing loss in mammals.
There is also an opportunity to provide a composition and a method of treating hearing loss including the step of administering the composition that includes a specific combination of components having an additive effect that is equal to or greater than the sum of the effect of the individual components in treating hearing loss when used in biologically effective amounts.